You probably did not read the article, as it does not talk about smartphones being a substitute tool for some tasks we used to do using our brains. The study is

You probably did not read the article, as it does not talk about smartphones being a substitute tool for some tasks we used to do using our brains. The study is about the attention efforts required by our need to always check our phones for new information, you can view it like our attention being prisonnier of our phones with no extra resources left for other activities.